On the shape and orientation of the tail of Comet Kohoutek (1973f)     

Angelo Bernasconi  Giuseppe Forti  Luigi Pansecchi 《Icarus》1977,31(3):401-411

Twenty-two photographs of Comet Kohoutek (1973f) have been projected onto the comet's orbital plane under the assumption of a flat tail confined in that plane. The comet has a mixed-type tail; therefore the results concerning Type I and Type II components of the tail are presented separately. The axis of the Type I tail appears to sweep back and forth with respect to the prolonged radius vector in a rather periodical way. Interpretations advanced by some authors for the analogous case of Comet Burnham (1959k) are mentioned briefly. For the Type II tail, a comparison with a theoretical tail model by Sekanina has allowed us to establish when the onset of appreciable dust production occurred. Finally, mention is made of the fact that some peculiarities of the dust tail might be also explained by assuming a three-dimensional model.  相似文献   

Nature, distribution and origin of polycyclic aromatic hydrocarbons (PAHs) in the sediments of Olbia harbor (Northern Sardinia, Italy)   总被引：1，自引：0，他引：1  

De Luca G  Furesi A  Micera G  Panzanelli A  Piu PC  Pilo MI  Spano N  Sanna G 《Marine pollution bulletin》2005,50(11):1223-1232

The nature, origin and distribution of US EPA polycyclic aromatic hydrocarbons (PAHs) in the sediments of Olbia harbor (North Sardinia, Italy) were investigated by gas-chromatography/mass spectrometry (GCMS). PAH concentrations in the sediments (SigmaPAHs) ranged from 0.16 to 0.77 microg g(-1), indicating a homogeneously low level of pollution. A rather exceptional prevalence of low molecular weight PAHs was substantiated: nearly 80% of SigmaPAHs include naphthalene (15.19%) and phenanthrene (64.47%). Carcinogenic compounds were present in very low (BaP, BkF, BaA and DBA) or negligible (BbF and Inp) concentrations. As indicated by the Phen/Ant molar ratio, the main source of PAHs is petrogenic, probably due to oil spills from shipping. The low/high molecular weight ratio (ranging between 1.2 and 26) distinguishes the sediments of the tourist harbor from those of the commercial/industrial harbor. Moreover, a slight but meaningful pyrolytic contribution to pollution was found in the tourist harbor, which has the most polluted sediments in the whole harbor. Finally, good linear correlations were found between a selected PAH (Phen and Naph) and selected sums of PAHs (i.e. the total amount of the other 15 US EPA and the sum of low molecular weight PAHs).  相似文献   

A classification of particle motions in the equatorial plane of a gravitational monopole-quadrupole field in Newtonian mechanics and general relativity     

Angelo Armenti Jr. 《Celestial Mechanics and Dynamical Astronomy》1972,6(4):383-415

  相似文献   

The occurrence and significance of Pleistocene and Upper Pliocene sapropels in the Tyrrhenian Sea     

Kay-Christian Emeis  Angelo Camerlenghi  Judith A. McKenzie  Domenico Rio  Rodolfo Sprovieri 《Marine Geology》1991,100(1-4):155-182

Numerous sapropels and sapropelic strata from Upper Pliocene and Pleistocene hemipelagic sediments of the Tyrrhenian Sea show that intermittent anoxia, possibly related to strongly increased biological productivity, was not restricted to the eastern Mediterranean basins and may be a basin-wide result of Late Pliocene-Pleistocene climatic variability. Even though the sapropel assemblage of the Tyrrhenian Sea clearly originates from multiple processes such as deposition under anoxic conditions or during spikes in surface water productivity and lateral transport of organic-rich suspensates, many “pelagic sapropels” have been recognized. Stratigraphic ages calculated for the organic-rich strata recovered during ODP Leg 107 indicate that the frequency of sapropel formation increased from the lowermost Pleistocene to the base of the Jaramillo magnetic event, coinciding with a period when stable isotope records of planktonic foraminifera indicate the onset of climatic cooling in the Mediterranean. A second, very pronounced peak in sapropel formation occurred in the Middle to Late Pleistocene (0.73-0.26 Ma). Formainifers studied in three high-resolution sample sets suggest that changes in surface-water temperature may have been responsible for establishing anoxic conditions, while salinity differences were not noted in the faunal assemblage. However, comparison of sapropel occurrence at Site 653 with the oxygen isotopic record of planktonic foraminifers established by Thunell et al. (Proc. ODP, Sci. Results 107, 1990) indicates that sapropel occurrences coincide with negative δ¹⁸O excursions in planktonic foraminifers in thirteen of eighteen sapropels recognized in Hole 653A. A variant of the meltwater hypothesis accepted for sapropel formation in the Late Pleistocene eastern Mediterranean may thus be the cause of several “anoxic events” in the Tyrrhenian as well. Model calculations indicate that the amount of oxygen advection from Western Mediterranean Deep Water exerts the dominant control on the oxygen content in deep water of the Tyrrhenian Sea. Inhibition of deep-water formation in the northern Adriatic and the Balearic Basin by increased meltwater discharge and changing storm patterns during climatic amelioration may thus be responsible for sapropel formation in the Tyrrhenian Sea.  相似文献   

Analytical Quantification of Carbon Dioxide Exchange Mediated by Spume Droplets     

Iury Angelo Gonçalves  Valdir Innocentini 《Boundary-Layer Meteorology》2018,166(2):327-350

Tornado-like vortices are simulated in a large-scale Ward-type simulator to further advance the understanding of such flows, and to facilitate future studies of tornado wind loading on structures. Measurements of the velocity fields near the simulator floor and the resulting floor surface pressures are interpreted to reveal the mean and fluctuating characteristics of the flow as well as the characteristics of the static-pressure deficit. We focus on the manner in which the swirl ratio and the radial Reynolds number affect these characteristics. The transition of the tornado-like flow from a single-celled vortex to a dual-celled vortex with increasing swirl ratio and the impact of this transition on the flow field and the surface-pressure deficit are closely examined. The mean characteristics of the surface-pressure deficit caused by tornado-like vortices simulated at a number of swirl ratios compare well with the corresponding characteristics recorded during full-scale tornadoes.  相似文献   

Water and soil quality at two eastern-Kentucky (USA) coal fires     

Trent Garrison  James C. Hower  Alan E. Fryar  Elisa D’Angelo 《Environmental Earth Sciences》2016,75(7):574

  相似文献   

Spatial analysis of clay content in soils using neurocomputing and pedological support: a case study of Valle Telesina (South Italy)     

Giuliano Langella  Angelo Basile  Antonello Bonfante  Florindo Antonio Mileti  Fabio Terribile 《Environmental Earth Sciences》2016,75(20):1357

  相似文献   

Macrofaunal succession in sediments around kelp and wood falls in the deep NE Pacific and community overlap with other reducing habitats     

Angelo F. Bernardino  Craig R. Smith  Amy Baco  Iris Altamira  Paulo Y.G. Sumida 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(5):708-723

Sunken parcels of macroalgae and wood provide important oases of organic enrichment at the deep-sea floor, yet sediment community structure and succession around these habitat islands are poorly evaluated. We experimentally implanted 100-kg kelp falls and 200 kg wood falls at 1670 m depth in the Santa Cruz Basin to investigate (1) macrofaunal succession and (2) species overlap with nearby whale-fall and cold-seep communities over time scales of 0.25–5.5 yr. The abundance of infaunal macrobenthos was highly elevated after 0.25 and 0.5 yr near kelp parcels with decreased macrofaunal diversity and evenness within 0.5 m of the falls. Apparently opportunistic species (e.g., two new species of cumaceans) and sulfide tolerant microbial grazers (dorvilleid polychaetes) abounded after 0.25–0.5 yr. At wood falls, opportunistic cumaceans become abundant after 0.5 yr, but sulfide tolerant species only became abundant after 1.8–5.5 yr, in accordance with the much slower buildup of porewater sulfides at wood parcels compared with kelp falls. Species diversity decreased significantly over time in sediments adjacent to the wood parcels, most likely due to stress resulting from intense organic loading of nearby sediments (up to 20–30% organic carbon). Dorvilleid and ampharetid polychaetes were among the top-ranked fauna at wood parcels after 3.0–5.5 yr. Sediments around kelp and wood parcels provided low-intensity reducing conditions that sustain a limited chemoautrotrophically-based fauna. As a result, macrobenthic species overlap among kelp, wood, and other chemosynthetic habitats in the deep NE Pacific are primarily restricted to apparently sulfide tolerant species such as dorvilleid polychaetes, opportunistic cumaceans, and juvenile stages of chemosymbiont containing vesicomyid bivalves. We conclude that organically enriched sediments around wood falls may provide important habitat islands for the persistence and evolution of species dependent on organic- and sulfide-rich conditions at the deep-sea floor and contribute to β and γ diversity in deep-sea ecosystems.  相似文献   

Preface     

Monica Pondrelli  Ken Tanaka  Angelo Pio Rossi  Enrico Flamini 《Planetary and Space Science》2011,59(11-12):1113

  相似文献   

Chemometric study of functional groups in Pennsylvanian gymnosperm plant organs (Sydney Coalfield, Canada): Implications for chemotaxonomy and assessment of kerogen formation     

Jos A. D&#x;Angelo  Erwin L. Zodrow  Alejandra Camargo 《Organic Geochemistry》2010,41(12):1312-1325

  相似文献